(a) Technical Field of the Invention
The present invention pertains to an electric medical thermometer and a specific method of analyzing temperature signals integrated into the electric medical thermometer.
(b) Description of the Prior Art
At present there are various types of thermometers for measuring body temperature, of which are mainly metal-in-liquid thermometers and electric thermometers using infrared ray or heat conducting technology.
The metal-in-liquid thermometer adopts the principle that substance expands with heat and contracts with cold to measure body temperature. These kinds of thermometers are sealed and packaged in glass tubes mainly using mercury as its measuring medium. Because of the toxic nature of mercury and the fragile nature of glass tubes, mercury units are relatively unsafe. Generally, electric thermometers can be divided into two classes: infrared ray measuring and heat conducting electric thermometers. The infrared varieties make temperature measurements through the human ear within one second of contact and can store multiple temperature measurements as data. Heat conducting electric thermometers are suitable for traditional measuring performed in the mouth, in the armpit, or at the rectum to obtain body temperature readings with a permissible error not greater than 0.1° C. Electric thermometers may incorporate multiple buttons that perform tasks such as power-on/off, temperature measuring, data saving, data look-up, and so on. Temperature measuring is initiated by depressing the corresponding button. A subsequent digital signal of the temperature reading is demonstrated on a liquid crystal display.
Generally, current electric thermometers function with the purpose of analyzing temperature signals received during the measuring process to generate a measurement of body temperature.
For example, in most of current heat conducting electric thermometers, the resistance of the sensor is sensitive to temperature and the sampling period is fixed and linear during measuring body temperature. Normally, the sampling frequency of those electric thermometers in measuring process is a sole frequency of approximate one second per cycle. When the sensor reaches thermal equilibrium while measuring, a temperature measurement is therefore shown on the liquid crystal display.
In reality, human's and most mammal's temperatures stay relatively constant. In the human body, muscle tissue is responsible for producing heat energy, which is consequently distributed along the circulatory system. At fixed frequency, the heart's systolic period sends blood out of the ventricle. Subsequently, the diastolic period rushes blood in from the circulatory system into the ventricle. Therefore, blood enters the arteries predictably wave after wave. Heat energy is transmitted through the circulatory system in all humans and mammals by the systole and diastole processes of the heart. Current electric thermometers take measurements with a sole frequency of one second per cycle. Surface skin temperature in the cavity will continually be shifted onto the measuring tip of the thermometer while vasoconstriction at the contact area will cause pressure build up for the next systolic and diastolic cycle. However, it is clear that average heart beat pulse does not function at the rate of one second per cycle. That means thermal compensation distributed along the circulatory system in wave after wave does not function as well at the rate of one second per cycle.
Therefore, if an electric medical thermometer takes the heart beat pulse as the sampling frequency instead of using the frequency of one second per cycle, more stable temperature signals while thermal compensating are attained. And therefore, more precise and reliable temperature measurement can be achieved, owing to the fact that existing electric medical thermometers reach thermal equilibrium defined by detecting a temperature increase no greater than 0.1° C. or 0.05° C. within a sampling period of 4 or 8 seconds and with a sampling frequency of one second per cycle. The problem of inconsistent measurements becomes apparent due to measurements being made at contrasting phases of the normal heart beat cycle such as a trough point or a crest point. The influence of this flaw is pronounced when said defined thermal equilibrium is approached. Consequently, electric medical thermometers appear in general medical tests with a difference of between 0.1 to 0.2 degree Celsius comparing to medical thermometers of Mercury.